AD8340 datasheet(12/20 Pages) AD

12 / 20 page

AD8340

Rev. 0 | Page 12 of 20

APPLICATIONS

USING THE AD8340

The AD8340 is designed to operate in a 50 Ω impedance

system. Figure 30 illustrates an example where the RF input is

driven in a single-ended fashion while the differential RF out-

put is converted to a single-ended output with a RF balun. The

baseband controls for the I and Q channels are typically driven

from differential DAC outputs. The power supplies, VPRF and

VPS2, should be bypassed appropriately with 0.1 µF and 100 pF

capacitors. Low inductance grounding of the CMOP and CMRF

common pins is essential to prevent unintentional peaking of

the gain.

RF INPUT AND MATCHING

The input impedance of the AD8340 is defined by the charac-

teristics of the polyphase network. The capacitive component of

the network causes its impedance to roll-off with frequency

albeit at a slower rate than 6 dB/octave. By using matching

inductors on the order of 5.6 nH in series with each of the RF

inputs, RFIP and RFIM, a 50 Ω match is achieved with a return

loss of >10 dB over the operating frequency range. Different

matching inductors can improve matching over a narrower

frequency range. The single-ended and differential input

impedances are exactly the same.

Ω

100pF

RFIM

RFIP

PHASE

5.6nH

100pF 5.6nH

~1VDC

Figure29.RFInputInterfacetotheAD8340Showing

CouplingCapacitors andMatchingInductors

The RFIP and RFIM should be ac-coupled through low loss

series capacitors as shown in Figure 29. The internal dc levels

are at approximately 1 V. For single-ended operation, one input

is driven by the RF signal while the other input is ac grounded.

DSOP

VPS2

VPRF

CMRF

RFIM

RFIP

CMOP

RFOM

RFOP

QFLP

CMOP

CMRF

VPRF

IFLP

AD8340

C12

(SEE TEXT)

C11

(SEE TEXT)

0.1

µF

5.6nH

100pF

5.6nH

100pF

IBBM

IBBP

INPUT

QBBP

QBBM

120nH

C14

0.1

µF

C10

0.1

µF

C18

100pF

C17

100pF

ETC1-1-13

OUTPUT

DISABLE

0.1

µF

0.1

µF

100pF

Figure30.BasicConnections

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